Estudo da adição de nióbio em diamante policristalino (PCD) obtido via alta pressão e alta temperatura (HPHT)

Abstract

The main objective of the studies developed in this work was to verify the influence of the variation of the niobium concentration as binder on the mechanical properties and wear resistance of the polycrystalline-niobium diamond system prepared by HPHT. This compound has great applicability in several areas of engineering, such as aeronautics, civil, metallurgical, being widely used as a cutting and drilling tool. The studied concentrations of niobium were 2.5%, 5.0% and 10% w.t.. High energy milling in Spex type mill was used to reduce the initial particle size of the PCD and for its mixture with the niobium, the effects of reduction of the average particle size verified were to values of 35.01 μm, 32.91 μm and 31.91 μm (for, respectively, the concentrations of 2.5%, 5.0% and 10% w.t. of niobium as binder). The HPHT conditions used for the consolidations of cylindrical samples 5 mm in diameter by 5 mm in height were the temperature of 1750°C, the pressure of 7.7 GPa and three cycles of 3 minutes. The measured values of relative density obtained were higher than ninety percent and the samples showed good integrity, not showing graphitization effects. For the PCD with concentrations of 2.5%, 5.0% and 10% w.t. of niobium as binder, relative density values of 3,37 g/cm³, 3,61 g/cm³ e 3,64g/cm³ and elasticity moduli of 946 GPa, 998.4 GPa and 1196 GPa. Good dispersion of the metal phase was observed both on the surfaces and inside of the specimens, and it was also observed that the increase in the amount of binder allowed a greater tendency to the occurrence of intergranular rupture than to the cleavage. The tribological tests on pinon-disc apparatus with a load of 150 N and rotation of 500 rpm allowed to observe that, when interacting with steel (with abrasion being observed as the predominant mechanism of wear), the wear trend is higher than in the case of its interaction with aluminum (where the great occurrence of adhesion was seen). The concentration of 10% of niobium as binder ensured lower wear resistance of the compound than that of 2.5%, in addition also higher values of temperatures were observed in regions close to the contact of the tribological pair.